Hot gas blowing fan

ABSTRACT

A hot-gas blowing fan includes a heat resisting impeller, a bearing, a heat insulting layer, a cooling portion, first and second magnetic couplings, a non-magnetic partition wall, and a collar. The heat insulating layer is disposed between the impeller and the bearing. The impeller and bearing are attached to the rotating shaft. The cooling portion is disposed between the heat insulating layer and the bearing. The cooling portion includes a cooling fluid that does not contact the bearing or the rotating shaft. The collar is positioned between the heat insulating layer and the impeller and is positioned between the heat insulating layer and the rotating shaft. The collar is made of a different material than the heat insulating layer.

TECHNICAL FIELD

The present invention relates to a hot-gas blowing fan applicable mainlyto a solid oxide fuel cell.

BACKGROUND ART

For various kinds of furnace for heating or firing, a hot-gas blowingfan is in some cases used for circulating or agitating the gas in thefurnace to homogenize the temperature in the furnace and improve theheating efficiency.

In a solid oxide fuel cell, the working temperature for power generationis from 700 to 1,000° C. Therefore, hydrogen and fuel gas such asnatural gas or coal gas as a supply source of carbon oxide, which becomefuel, are heated to from 700 to 1,000° C. before supplying them to thefuel electrode of the fuel cell.

In this case, it is reported to use a so-called steam reformation methodwherein the hot fuel gas and steam are reacted to produce pure hydrogenaccording to the following formula, before supplying them to the fuelelectrode. This method improves the reaction efficiency of the fuel gasand increases power generation efficiency in comparison with a methodthat the fuel gas is straightly fed to the fuel electrode for reaction.(Reaction formula of the steam reformation) CH₄+2H₂O→CO₂+4H₂

In order to carry out the steam reformation of the fuel gas, it isnecessary to humidify the fuel gas. However, when the humidification iscarried out by using water for industrial use or domestic use,impurities contained in the water contaminate or corrode the main bodyof the fuel cell, so that a significant negative impact is on theperformance and durability of the fuel cell main body. Further, anattempt to install an equipment for removing completely the impuritiesin the water supply line was questionable in view of the installationspace and initial investment, and therefore, was not realistic.

In the solid oxide fuel cell, water is produced as a reaction product byhydrogen and oxygen at the side of the fuel electrode to which a fuelgas is supplied. Namely, at the same time that the fuel gas suppliedtoward the fuel electrode reacts at the fuel electrode, it is humidifiedwith the produced water. The produced water does not contain impurities.Accordingly, if the humidified fuel gas can be circulated for reuse, thesteam reformation of a fuel gas by the humidification becomes possiblebefore the reaction, whereby the power generation efficiency can beincreased.

Further, for the fuel gas heated to from 700 to 1,000° C. to be suppliedto the fuel electrode, it is impossible that hydrogen and carbon oxideas reactive gases can be reacted entirely in only once contact with thefuel electrode. By circulating the fuel gas for reusing, the fuel gascan be used effectively and the sensible heat of the fuel can be reused,whereby the power generation efficiency can be increased in this pointalso.

From the reason described above, the technique of using a hot-gasblowing fan for a solid oxide fuel cell to circulate a hot fuel gas hasbeen studied intensively.

On the other hand, there can be considered to provide a structure thatthe temperature of a hot fuel gas is decreased to about 100° C. by meansof a heat exchanger, and when the temperature is not more than 100° C.,the fuel gas is pressurized with an ordinarily available fan, and thenthe fuel gas is heated again to a working temperature of from 700 to1,000° C. However, the idea of this structure was no realistic at allwhen the problems of heat loss, the cost of the heat exchanger and theinstallation space were considered.

When the hot-gas blowing fan is applied to the solid oxide fuel cell,the following conditions should be satisfied.

1) Since a hot fuel gas is combustible and is deadly to human beingdepending on a fuel cell used, the hot fuel gas must not be leakedoutside the system. Namely, the shaft sealing device for the rotatingshaft connecting the motor with the impeller comprising rotary vanes anda disk should be completely gas-tight.

2) Since there is a case that the fuel cell is used as a dispersed powersource in out-country, and the fuel cell system itself should be simple,the utility should not be used other than a d.c. power source suppliedfrom the fuel cell system itself. Further, the amount of electric powerfor the blowing fan should be not more than about 5% of the generatedpower.

3) The fuel cell is installed as a dispersed power source for usualhouses and small-sized apartments. Accordingly, the blowing fan usedshould be compact.

4) The initial investment should be low. Specifically, it is desired tobe not more than 3% of the sales price of the fuel cell system.

5) In order to prevent condensation of the hot fuel gas, the temperatureof the part exposed to the hot fuel gas should be always at least thedew-point temperature.

6) In order to prevent the breakage or deformation of the impeller,there should not be any danger of collision of a foreign matter having asize by which the breakage or deformation of the impeller during therotation may cause.

As described above, from the viewpoints of safeness and economy, it isimportant for the solid oxide fuel cell that the hot fuel gas should notbe leaked outside the system.

As the shaft sealing method for the hot-gas blowing fan, which hasconventionally been utilized, there is a method that a first shaftsealing device is inserted on the rotating shaft at a position between abearing and a cooling portion provided between an insulating layer andthe bearing, and a second shaft sealing device is inserted on therotating shaft at a position between a second bearing disposed at alow-temperature side of the rotating shaft and a shaft coupling disposedat the end of the rotating shaft, this method being generally utilized.As the first and/or second shaft sealing device, a gland packing, an oilseal, an O-ring, a labyrinth, a mechanical seal or the like is used.

Among these shaft sealing devices, the gland packing, the oil seal andthe O-ring are made of rubber or a synthetic resin. Accordingly, theseelements are sensitive to gas quality and temperature, and therefore,the service life can not be expected beyond several years. Especially,the solid oxide fuel cell has strong reducing properties because the hotfuel gas as fuel contains hydrogen and carbon oxide. Accordingly, thesealing technique using rubber or a synthetic resin is less reliability.

For the labyrinth or the mechanical seal, a purge gas is used to alwayspush it in order to prevent a process gas sealed inside from leakingoutside. In this case, the mixing of the purge gas with the process gasis unavoidable. For the solid oxide fuel cell, it is very important thatthe process gas should be pure for the performance of the fuel cell, andthe mixing of the purge gas is generally impermissible. In case of usinga purge gas for the solid oxide fuel cell, an inert gas such asnitrogen, helium or the like being expensive can be considered. However,the cost of the utility would thereby increase, with the result of anincrease of cost per unit power. Further, when the solid oxide fuel cellis used as a dispersed power source for a usual house and a small-sizedapartment, there arise problems such as the space for the purge gascylinder, safety control, re-supply and so on, such being unrealistic.

As described above, any shaft sealing device without using the utilityother than the power source, being compact, simple and completelygas-tight has not actually been proposed.

A bearing is fitted to the rotating shaft to cantilever the impeller.The upper temperature limit for allowing use of the bearing for along-term under good conditions would be about 100° C. in considerationof the restriction of the upper temperature limit of the lubricant suchas grease used for lubricating the bearing. It is necessary to removethe flux of heat transferred from the impeller to the rotating shaftthrough the heat insulating layer disposed between the impeller and thebearing, whereby the bearing can be cooled to a predeterminedtemperature or lower. Here, the removal of heat means that the flux ofheat is taken to discharge it.

In the hot-gas blowing fan conventionally used for removing heat, such amethod is generally employed, wherein a water-cooling jacket is providedbetween the bearing and the impeller which is directly exposed to a hotgas, in coaxial with the rotating shaft and in contactless therewithwhile it is in direct contact with the outer ring of the bearing, acooling water cooled to, for example, not more than 30° C. is suppliedto the water-cooling jacket to maintain the surface temperature of thewater-cooling jacket to, for example, not more than 50° C. whereby therotating shaft is cooled by heat radiation, and the bearing is cooled bythe heat transfer between the water-cooling jacket and the outer ring ofthe bearing. Further, such a method may be employed, wherein thelubricating oil cooled to, for example, not more than 30° C. is broughtto direct contact with the rotating shaft and the bearing to remove theheat under lubrication.

However, the conventional cooling method required devices such as a pumpfor circulating water or a lubricating oil as a heat-removing medium, acooling device for cooling the heat-removing medium and pipes forconnecting these, with the result of bringing drawbacks of making theentire system complicated and hindering the reduction of theinstallation space. In particular, such were the major negative factorsin introducing the solid oxide fuel cell as a dispersed power source fora usual house or a small-sized apartment.

In the solid oxide fuel cell using natural gas as the fuel, thedew-point of the fuel gas, i.e., the process gas is about 70° C.Accordingly, when the heat-removing medium such as water or alubricating oil having a low temperature as above-mentioned was used,there caused super-cooling and there caused dew condensation on and neara cooling section such as the water-cooling jacket, so that therecreated a problem of causing the deterioration of the fuel cell mainbody due to corrosion derived from the condensation of moisture, andelution or scattering of a contaminant to thereby affect deadly theperformance and durability of the fuel cell.

Further, since it was necessary to prevent the deterioration of thewater or the lubricating oil as the heat-removing medium and tocompensate the reduced amount thereof, a continuous, maintenance-freeoperation of, for example, 24 hours×365 days×3 years was considered tobe difficult.

In addition, if the power source for a device such as a pump forcirculating the heat-removing medium is stopped due to power stoppage,or the supply of the heat-removing medium is stopped due to a failure ofthe device itself, measures have to be taken so as to stop the heatingof the hot gas by means of an electric control mechanism or the like. Insuch case, the shaft sealing device or the bearing may suffer a fataldamage by the heat of the hot gas of from 700 to 1,000° C. inside thedevice or the heat from the heat insulating material heated to have ahigh temperature.

Further, a method in which the rotating shaft and the bearing are cooleddirectly with use of a cooling fan can be considered, as one way ofthinking, although the sealing structure for the method is notrealistic. In this case, the heat transfer coefficient indicating theability of removing heat, of water is from 1,000 to 3,000 w/m²K whilethat of air is far smaller, i.e. from 10 to 30 w/m²K. Accordingly, ifair is used to obtain the same cooling effect as that by water, thesurface area of the heat-removing portion should be about from 100 to300 times as much as the case of using water, and it was in factdifficult to provide the heat-removing section in a limited space aroundthe rotating shaft and the bearing.

When a hot-gas blowing fan is used for the solid oxide fuel cell, it isnecessary to drive a small-sized impeller at a high speed, rather thandriving a large-sized impeller at a low speed, to satisfy specificationssuch as wind volume, wind pressure and so on in view of restrictionssuch as cost and the installation space. However, if a foreign matterhits the impeller rotated at a high speed, the impeller may be broken ordeformed.

For example, when an impeller made of silicon carbide is used to driveit at an impeller's circumferential velocity of 205 m/sec, the allowableparticle size of foreign matter which does not cause the breakage of theimpeller even in collision, is not more than 1 mm according toexperiments. It means that it is necessary to provide a dust collectornot to suck a foreign matter having a particle size of more than 1 mmfrom the inlet port of the scroll under the above-mentioned condition.

Conventionally, the purpose of use of the hot-gas blowing fan was fairlylimited; in particular, it was unnecessary to consider the incoming of aforeign matter. Accordingly, a dust collector for a hot-gas blowing fanrequiring a low cost and a small installation space has not actuallyexisted.

From these reasons, it was difficult to provide the technique capable ofsatisfying the conditions to apply a hot-gas blowing fan to theabove-mentioned solid oxide fuel cell.

It is an object of the present invention to solve the problems of theconventional techniques and to provide a hot-gas blowing fan suitablefor a solid oxide fuel cell.

DISCLOSURE OF THE INVENTION

The present invention is to achieve the above-mentioned object, and toprovide the hot-gas blowing fan described below.

(1) A hot-gas blowing fan comprising a heat resisting impellercantilevered by a rotating shaft, a bearing attached to the rotatingshaft, a heat insulating layer disposed between the impeller and thebearing and a cooling portion disposed between the heat insulating layerand the bearing, wherein a first coupling to be mated with anothermagnetic coupling is disposed on the shaft end of the rotating shaft atthe side opposite to the impeller and a non-magnetic partition wall isdisposed between the first coupling and a second coupling to be matedwith the first magnetic coupling is disposed on the shaft end of thedriving shaft of a motor, whereby a space surrounding the rotating shaftis hermetically sealed from an outer field by the non-magnetic partitionwall and a casing.

(2) The hot-gas blowing fan according to the above-mentioned (1),wherein an inert gas is filled in the hermetically sealed space.

(3) A hot-gas blowing fan comprising a heat resisting impellercantilevered by a rotating shaft, a bearing attached to the rotatingshaft, a heat insulating layer disposed between the impeller and thebearing, which further comprises an air cooling means comprising a heatreceiving portion disposed between the heat insulating layer and thebearing, an air cooling/radiating portion provided at an outer side of acasing and a heat transporting portion connecting the heat receivingportion to the air cooling/radiating portion.

(4) The hot-gas blowing fan according to the above-mentioned (3),wherein the heat receiving portion and the heat transporting portion areunified to form a thermo-siphon heat pipe.

(5) The hot-gas blowing fan according to the above-mentioned (1),wherein the cooling portion is an air cooling means comprising a heatreceiving portion disposed between the heat insulating layer and thebearing, an air cooling/radiating portion provided at an outer side ofthe casing and a heat transporting portion connecting the heat receivingportion to the air cooling/radiating portion.

(6) The hot-gas blowing fan according to any one of the above-mentioned(1) to (5), wherein an inertia dust collector is provided at the inletport of a scroll.

(7) The hot-gas blowing fan according to any one of the above-mentioned(1) to (6), which is used for a solid oxide fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a side of the hot-gas blowing fanaccording to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a side of the hot-gas blowing fanaccording to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a side of the hot-gas blowing fanaccording to a third embodiment of the present invention.

FIG. 4 is a cross-sectional view of a side of the hot-gas blowing fanaccording to a fourth embodiment of the present invention.

FIG. 5 is a diagram viewed from a side of P arrow mark in FIG. 4.

FIG. 6 is a cross-sectional view of a plane of the hot-gas blowing fanaccording to a fifth embodiment of the present invention.

FIG. 7 is a diagram viewed from a side of Q arrow mark in FIG. 6.

FIG. 8 is a cross-sectional view taken along a line X-X in FIG. 7.

FIG. 9 is a cross-sectional view of a side of the hot-gas blowing fanaccording to a sixth embodiment of the present invention.

FIG. 10 is a cross-sectional view of a side of the hot-gas blowing fanaccording to a seventh embodiment of the present invention.

FIG. 11 is a side view of a conventional hot-gas blowing fan.

EXPLANATION OF REFERENCE NUMERALS

1: Scroll, 2: Inlet port of scroll, 3: Impeller, 4: Discharge port ofscroll, 5: Cooling portion, 6: Rotating shaft, 7: Bearing, 8: Outer heatretaining layer, 9: Fan shaft side magnetic coupling, 10: Motor shaftside magnetic coupling, 11: Non-magnetic partition wall, 12: Casing, 13:Fitting flange, 14: Cooling water supply side pipe, 15: Cooling waterdischarge side pipe, 16: Heat insulating layer, 17: Second bearing, 18:Permanent magnet located on fan shaft side magnetic coupling, 19:Permanent magnet located on motor shaft side magnetic coupling, 20:O-ring, 21: Backboard collar, 21 a: Backboard, 21 b: Collar, 22: Heatinsulating spacer, 23: Motor, 24: Back-to-back duplex angular bearing,25: Purge gas inlet, 26: Purge gas outlet, 27: Shaft sealing device, 28:Heat receiving portion, 29: Heat transporting portion, 30: Aircooling/radiating portion, 31: Cooling fan, 32: Fin, 33: Evaporativeportion, 34: Heat transporting pipe, 35: Enclosed water, 36: Shielding,37: Apertured portion, 38: Shielding supporter, 39: First shaft sealingdevice, 40: Second shaft sealing device, 41: Shaft coupling, 42: Purgegas inlet

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, some embodiments of the present invention will bedescribed with reference to the drawing.

FIG. 1 is a cross-sectional view of a side of the hot-gas blowing fanaccording to an embodiment of the present invention wherein referencenumeral 1 designates a scroll, 2 an inlet port of scroll, 3 an impeller,4 a discharge port of scroll, 5 a cooling portion, 6 a rotating shaft, 7a bearing, 8 an outer heat retaining layer, 9 a fan shaft side magneticcoupling, 10 a motor shaft side magnetic coupling, 11 a non-magneticpartition wall, 12 a casing, 13 a fitting flange, 14 a cooling watersupply side pipe, 15 a cooling water discharge side pipe, 16 a heatinsulating layer, 17 a second bearing, 18 a permanent magnet located onthe fan shaft side coupling 9, 19 a permanent magnet located on thewater shaft side magnetic coupling 10 so as to face the permanent magnet18 located on the fan shaft side coupling 9, 20 an O-ring, 21 abackboard collar, 21 a a backboard, 21 b a collar, 22 a heat insulatingspacer and 23 a motor, respectively.

In FIG. 1, a hot-gas is sucked through the inlet port 2 of the scroll 1,the pressure of the hot-gas is increased by the revolution of theimpeller 3 comprising rotary vanes and a disk and the gas is dischargedthrough the discharge port 4. Accordingly, the temperature of theimpeller 3 reaches a temperature level of, for example, 700° C. orhigher which is equal to the temperature of the hot-gas. Such a highrevolution under a high temperature creates a large centrifugal stressat, in particular, the root of the rotary vanes of the impeller 3.

Further, since the hot fuel gas as a hot gas used for a solid oxide fuelcell contains 30 to 50% of water vapor in volume ratio, care todeterioration of the strength of the materials due to oxidation by hotwater vapor has to be taken.

Accordingly, the impeller 3 in direct contact with the hot gas or theimpeller 3 and the rotating shaft 6 have to be made of a material havinga sufficient strength in a high temperature atmosphere and beingexcellent in durability to oxidation by hot water vapor. In thisembodiment, Incoloy (trademark) 800H being a Fe—Ni—Cr alloy is employedfor the impeller 3 and the rotating shaft 6. However, a Ni—Cr—Co alloyor the like is sometimes used. More preferably, a ceramic material suchas silicon carbide, silicon nitride, sialon or the like having a densityof not more than 10% in porosity may be employed.

The cooling portion 5 is a water-cooling jacket in this embodiment andis disposed in a state of being coaxial with the rotating shaft 6 andfurther in a state of contacting directly to the outer ring of thebearing 7. In this embodiment, cooling water cooled to, for example, 70°C. is supplied to the water-cooling jacket to maintain the surfacetemperature of the water-cooling jacket to be, for example, 80° C. whichis higher than 70° C. as the dew-point of the hot gas whereby therotating shaft 6 is cooled by a radiation effect and the bearing 7 iscooled by heat conduction. Accordingly, the dew condensation does nottake place at the inside and the bearing 7 can be kept to the permissivetemperature or lower whereby the hot-gas blowing fan can stably be usedfor a long time. It is preferred that the temperature of the suppliedcooling water is higher than the temperature of the dew-point of aprocess gas in operation, more preferably, the temperature of thesupplied cooling water is determined at least 5° C. higher than thetemperature of the dew-point of the process gas in operation. Further,in this embodiment, the rotating shaft 6 extends vertically; theimpeller 3 is disposed in an upper portion of the shaft and the motor 23is disposed at a lower portion thereof. Accordingly, there is a casethat bubbles remain in an upper portion of the cooling water conduit ofthe water-cooling jacket whereby the cooling power at thebubble-remaining portion decreases. Therefore, means for removingbubbles are disposed in an upper portion of the cooling water conduitalthough not shown.

The cooling water is circulated by means of a pump (not shown) and iscooled to 70° C. by means of a cooling device (not shown).

The backboard collar 21 comprises a backboard 21 a covering the rearsurface of the rotating portion of the impeller 3 and a collar 21 bdisposed in coaxial with the rotating shaft 6 and in non-contacttherewith. The backboard 21 a and the collar 21 b are jointed each otherby means of socket and spigot joint or the like and a centering device(not shown) so that they can be thermally expanded while their commoncenter can be maintained. The backboard 21 a forms the flow path of hotgas inside the hot-gas blowing fan in association with the scroll 1. Asthe material for the heat insulating layer 16, ceramic fibers or thelike are used. On the other hand, the backboard collar 21 preventsceramics fibers from scattering into the flow path of hot gas. As shownin FIG. 1, there is no seal positioned between the impeller 3 and thebearing 7 to prevent gas in the hot flow path from traveling from theimpeller 3 to the bearing 7. The backboard collar 21 is fixed to thecooling portion 5 by interposing the heat insulating spacer 22therebetween. The backboard 21 a contacts directly the hot gas wherebyit has the same temperature level as the hot gas. The collar 21 b isformed integrally with the backboard 21 a and the presence of the heatinsulating spacer 22 between the collar 21 b and the cooling portion 5blocks the cooling effect from the cooling portion 5. Accordingly, thecollar 21 b has a temperature level near the temperature of thebackboard 21 a. Thus, the thermal deformation due to a temperaturedifference between the backboard 21 a and the collar 21 b can beprevented and at the same time, the thermal loss of the fuel cell systemcan be reduced.

As the material for the backboard 21 a and the collar 21 b, stainlesssteel, heat-resistant cast steel or ceramics having a sufficientstrength at a high temperature and durability to oxidation by hot watervapor may be used. In this embodiment, SUS316 is used. As the materialfor the heat insulating spacer 22, ceramics of low heat conduction suchas Codilite, aluminum titanate may be used. In this embodiment, Codiliteis used. Further, it is possible that the collar 21 b is made of the lowthermal conduction ceramic to perform the function of the heatinsulating spacer 22.

A fan shaft side magnetic coupling 9 as a first coupling to be matedwith another magnetic coupling is attached to the shaft end of therotating shaft 6 at the opposite side of the impeller 3. A motor shaftside magnetic coupling 10 as a second coupling is attached to the shaftend of the motor shaft so as to face the first coupling. Between the fanshaft side magnetic coupling 9 and the motor shaft side magneticcoupling 10, a clearance of from about 3 to 10 mm is provided, theclearance being determined from the relation between the magnetic forceand the torque transmission. In the clearance, a non-magnetic partitionwall 11 of non-air-permeability made of a material such as plastic,non-magnetic ceramic, Bakelite or the like is disposed, and a sealingmaterial such as an O-ring 20, a gasket or the like is disposed at acontact portion of the casing 12 and the non-magnetic partition wall 11.The casing 12 mentioned herein is a structural body supporting thesecond bearing 17 and the non-magnetic partition wall 11. However, thecasing in the present invention includes a structural body covering thecooling portion 5 and a heat receiving portion 28 (see FIG. 4) whichwill be described hereinafter. The casing 12 and the fitting flange 13,and the scroll 1 and the fitting flange 13 have respectively flangeconnection, and a sealing material such as an O-ring, a gasket or thelike is provided in each connection surface although they are not shownin the drawing. Sealing devices (not shown) are also provided betweenthe cooling water supply side pipe 14 and the fitting flange 13 andbetween the cooling water discharge side pipe 15 and the fitting flange13. For the permanent magnet 18 used for the fan shaft side magneticcoupling 9 and the permanent magnet 19 used for the motor shaft sidemagnetic coupling 10, a rare earth-cobalt magnet is preferably usedbecause of its having excellent heat stability and corrosionresistivity.

With the above-mentioned structure, an enclosed space is formed by thecombination of the casing 12 and the non-magnetic partition wall 11. Thesealing portion in the enclosed space is provided by the casing 12 andthe non-magnetic partition wall 11 as fixed parts, and the sealingportion is cooled sufficiently in terms of temperature. Accordingly, acompletely gas-tight seal is possible with an inexpensive sealingmaterial such as an O-ring, a gasket, a liquid gasket or the like.

Namely, since the enclosed space can be formed by the casing 12 and thenon-magnetic partition wall 11, the hot-gas blowing fan is in acompletely gas-tight state with respect to an outer ambient atmospherewithout using a purge gas.

When the hot gas is combustible, the hot combustible gas invades intothe enclosed space to mix with air in the enclosed space. In thisembodiment, the volume of the enclosed space is designed so that even ifcombustion occurs, the amount of generated heat is sufficiently small incomparison with the heat discharged to the surroundings. If the pressureof a hot combustible gas becomes lower than the pressure of the enclosedspace due to any cause, there is a possibility that air in the enclosedspace leaks outside during the process whereby a local combustion or aslight contamination of the hot combustible gas takes place. However, itcan be handled sufficiently by minimizing the volume of the enclosedspace.

In applying the hot-gas blowing fan to a solid oxide fuel cell, when theprocess is to be stopped, the heating of a hot fuel gas as the processgas heated to from 700 to 1,000° C. during operation is stopped todecrease the temperature. In this case, since the process gas has alarge heat capacity, the temperature decreases gradually, and since theinternal gas is substituted with non-condensable nitrogen or air, nocondensation of moisture takes place. When design is made so that thecasing 12 is exposed to ambient air, the temperature of the entirecasing decreases rapidly because the casing 12 has a small heat capacitywhereby the temperature of the remained process gas containing watervapor difficult to be substituted in the enclosed space decreases alsorapidly. The outer heat retaining layer 8 lined on the outer wall of thecasing is provided to eliminate such trouble. Namely, the outer heatretaining layer 8 made of a heat insulating material such as ceramicfibers is mounted on the outer periphery of the casing 12 to prevent thecasing from rapid cooling due to the ambient air. Accordingly, there islittle possibility of condensation of moisture in the enclosed space.

FIG. 2 is a cross-sectional view taken along a side plane of a secondembodiment of the present invention wherein the second bearing 17 inFIG. 1 is omitted and the bearing 7 is replaced by a back-to-back duplexangular bearing 24. On the same parts as in FIG. 1, which are notreferred to in this embodiment, those reference numerals are omitted.

The back-to-back duplex angular bearing 24 comprises a set of bearingsby which an axial load in either direction, a radial load and a momentload can be received simultaneously. Accordingly, the second bearing isunnecessary. In this embodiment, the distance between the back-to-backduplex angular bearing 24 and the fan shaft side magnetic coupling 9 ismade shorter and the volume of the enclosed space formed by thenon-magnetic partition wall 11 and the casing 12 can significantly bereduced as shown in FIG. 2. The enclosed space having a smaller volumeprovides the following advantage. Namely, even when the hot combustiblegas invades into the enclosed space to mix with the remaining air in theenclosed space, and in such case, even though combustion takes place,instantaneous heat dissipation occurs because the calorific value issmall. Accordingly, a problematic increase of inner pressure does notoccur. Further, requirements for reducing the size and the cost, whichare particularly important for the solid oxide fuel cell system, can bemet. The back-to-back duplex angular bearing 24 may be a double rowangular bearing.

FIG. 3 is a cross-sectional view taken along a side plane of a thirdembodiment of the present invention wherein a shaft sealing device 27, apurge gas inlet 25 and a purge gas outlet 26 are added in the embodimentshown in FIG. 1. On the same parts as in FIG. 1, which are not referredto in this embodiment, those reference numerals are omitted.

In FIG. 3, the purge gas inlet 25 and the purge gas outlet 26 areprovided in the enclosed space formed by the casing 12 and thenon-magnetic partition wall 11.

Before the initiation of operation to the hot-gas blowing fan, the airin the enclosed space is entirely discharged outside by means of thepurge gas inlet 25 and the purge gas outlet 26, and then, an inert gasis sealed in the enclosed space by sealing the purge gas inlet 25 andthe purge gas outlet 26. The shaft sealing device 27 is used effectivelyto prevent the decrease of the amount of the inert gas as the purge gasused or to eliminate the problem caused by the mixing of the inert gaswith the process gas. The inert gas sealed in the enclosed spaceeliminates a danger of combustion or explosion of the hot combustiblegas in this space. Further, there is little possibility of dewcondensation at the inside of the casing 12.

As described above, by sealing the inert gas in the enclosed spaceformed by the casing 12 and the non-magnetic partition wall 11, it ispossible to obtain a hot-gas blowing fan of completely gas-tight, whicheliminates dew condensation and a danger of combustion or explosion evenin a case of using a hot combustible gas containing moisture.

In FIG. 3, a gland packing is used as the shaft sealing device 27.However, an O-ring, a labyrinth, an oil seal or the like may be used.The non-magnetic partition wall 11 is required to be of a non-magneticmaterial in order to prevent a reduction of the torque transmissionefficiency due to an eddy current. For the non-magnetic partition wall11 shown in FIGS. 1 to 3, bakelite was used. As the inert gas, nitrogengas, argon gas, helium gas is preferably used.

FIG. 4 is a cross-sectional view taken along a side plane of a fourthembodiment of the present invention wherein reference numeral 1designates a scroll, 3 an impeller, 6 a rotating shaft, 7 a bearing, 27a shaft sealing device, 9 a fan shaft side magnetic coupling, 10 a motorshaft side magnetic coupling, 11 a non-magnetic partition wall, 12 acasing, 16 a heat insulating layer, 28 a heat receiving portion, 29 aheat transporting portion, 30 an air cooling/radiating portion, 31 acooling fan, respectively. FIG. 5 is a diagram viewed from a side of Parrow mark, which shows the heat receiving portion 28, the heatinsulating layer 16 and the fin 32 in cross section together with theheat transporting portion 29, the air cooling/radiating portion 30 andthe cooling fan 31.

The heat receiving portion 28 is disposed in coaxial with the rotatingshaft 6 and in non-contact therewith in an intermediate region betweenthe impeller 3 in direct contact with a hot gas and the bearing 7 so asto receive a heat flux to be thermally conducted via the rotating shaft6, directly from the rotating shaft 6 by radiation and convection and toreceive heat by heat conduction through the shaft sealing device 27 andthe bearing 7. Further, it receives heat of a heat flux thermallyconducted via the heat insulating layer 16 disposed between the impeller3 and the bearing 7. The heat receiving portion 28 is preferably made ofa material such as copper, a copper alloy, aluminum or an aluminum alloyhaving a high thermal conductivity. The heat transporting portion 29serves to transfer the heat received by the heat receiving portion 28 tothe air cooling/radiating portion 30 with good efficiency. For the heattransporting portion, a solid rod of copper, a copper alloy, aluminum oran aluminum alloy having a high thermal conductivity is sometimes used.In this embodiment, however, a heat pipe whose equivalent thermalconductivity is from several ten to several thousand times of thethermal conductivity of copper, of a high heat transportation capacity,was employed.

As the material for a container of heat pipe, there are copper, iron,stainless steel, aluminum and so on, and as the working liquid to besealed in the container, there are water, naphthalene, Dowtherm-A,methanol, ammonia, acetone, Fron-12 and so on. A variety of combinationthereof can be used. In this embodiment, however, copper is used as thematerial for the container and water is used as the sealed workingliquid. The operating temperature range of the heat pipe when copper andwater are used., is from 20 to 250° C. Accordingly, such combination canbe used preferably in this embodiment that the temperature of thebearing should be cooled to not more than 100° C. The way of removingheat by means of the heat pipe utilizes the latent heat of evaporationof the working liquid sealed under a reduced pressure. Since the latentheat of evaporation of water used as the working liquid is 2.2 J/kgwhich is the largest among other kinds of working liquid, a very highheat transportation capacity can be exhibited. The number of heat pipesis determined based on calculation from a heat quantity to be withdrawnand the maximum heat transportation quantity of the heat pipes. Thejoining portion of the heat pipes forming the heat transporting portion29 to the heat receiving portion 28 should be large in area as possiblein order to transfer the heat quantity received by the heat receivingportion 28 to the heat pipes effectively. Further, in order to reducethe thermal contact resistance at the joining portion, each heat pipe ispreferably fitted forcibly into a heat pipe fitting opening formed atthe heat receiving portion 28 to increase the effective contact area.Further, when it is forcibly inserted, grease of high thermalconductivity is preferably applied to the front surface of the heatpipe. Further, it is more preferable that a pipe material for the heatpipe is previously joined to the heat receiving portion 28 by means ofbrazing or welding and then the working fluid such as water is sealed inthe pipe.

The air cooling/radiating portion 30 is provided with a heat sinkcomprising a large number of fins 32. The water as the working liquidflows in the heat pipe and it evaporates at the heat receiving portion28, the vapor is transferred to the air cooling/radiating portion 30 dueto the partial pressure difference, the vapor transferred into the aircooling/radiating portion 30 condenses into water, and the condensedwater returns again to the heat receiving portion 28 due to thecapillary phenomenon by means of a wick structure or the like orgravity. Accordingly, it is preferable that the air cooling/radiatingportion 30 is disposed at a higher position than the heat receivingportion 28 despite the presence or absence of the wick structure or thelike.

Since the thermal conductivity of a water-cooling system is from 100 to300 times as the case of an air-cooling system, the total outer surfaceof the fins 32 is desirably not less than from 100 to 300 times as thesurface of the heat drawing portion of a conventionally usedwater-cooling type jacket in order to obtain the same coolingperformance as the water-cooling system. The heat pipe can be bent.Accordingly, even when the air cooling/radiating portion 30 can not bedisposed just above the heat receiving portion 28, the aircooling/radiating portion 30 can be disposed at relatively higherposition than the heat receiving portion 28 while a sufficientheat-radiating surface is obtainable, by bending optionally the heatpipe.

The fins 32 and the heat pipe are joined so that the heat pipepenetrates the substantially central portion of each fin whereby theheat transported by the heat pipe is transferred by thermal conductionuniformly to all fins. The heat flux transported from the heat receivingportion 28 to the heat transporting portion 29 is discharged intoatmosphere by the convective thermal conduction from the front surfaceof the fins 32 of the air cooling/radiating portion 30 via air. Thecooling fan 31 may be attached to the air cooling/radiating portion 30.When the fins 32 are subjected to forcibly cooling by air, i.e., aircooling, the convective thermal conductivity is increased to increasethe cooling capacity whereby the total outer surface of the fins can bereduced.

As the material for the fins 32 forming the air cooling/radiatingportion 30, use of copper, a copper alloy, aluminum or an aluminum alloyhaving a high thermal conductivity is desirable.

In this embodiment, the hot gas temperature is 850° C. In this case,when the total outer surface of the fins was to be 0.2 m² and air of 20°C. was passed between the fins at a flow rate of 5 m/sec by using thecooling fan, the convective thermal conductivity of the surface of finwas 12 w/m²K. As a result, the average temperature of the fins was 60°C. and the average temperature of the heat receiving portion was 80° C.whereby a temperature of not more than 100° C. as the initial targettemperature could be achieved. In this embodiment, the heat removingquantity was 96 w in calculation. In order to further equalize thetemperature distribution at the heat receiving portion 28, two heatpipes each having a maximum heat transporting quantity of 100 w wereused.

As described above, although the cooling performance can be improved byusing the cooling fan 31, a cooling system utilizing the naturalconvection of ambient air is possible without a forced air coolingsystem by using a cooling fan. In a case without using the cooling fanin the above-mentioned embodiment, the thermal conductivity of thesurface of the fins by natural convection was 8 w/m²K. As a result, theaverage temperature of the fins was 80° C. and the average temperatureof the heat receiving portion was 100° C.

In the solid oxide fuel cell, a d.c. power source provided by the fuelcell itself is used as the power source for the driving motor 23 for thehot-gas blowing fan and the cooling fan 31. Even when the operation ofthe fuel cell stops suddenly for any reason and the operations of thefan driving motor and the cooling fan are stopped, the cooling by thenatural convective thermal conduction continues whereby the over-heatingof the bearing 7 or the shaft sealing device 27 can easily be prevented.

The dew-point of the hot gas in this embodiment is 70° C. In thisembodiment, since the average temperature of the heat receiving portionis 80° C, i.e., higher than the dew-point, there is no dew condensationin the vicinity of the heat receiving portion 28.

However, when the temperature of outside air for cooling at the aircooling/radiating portion 30 is extremely low, there is possibility thatthe temperature of the heat receiving portion 28 is lower than thedew-point to cause dew condensation in the vicinity of the heatreceiving portion 28. Then, there are possibilities that condensed waterdrops infiltrate into the heat insulating layer 16 to causedeterioration of the heat insulating property or water drops come tocontact with the rotating shaft or impeller 3 of high-temperature tochange the temperature gradient from the impeller 3 to the rotatingshaft whereby an excessive thermal stress takes place in the impeller 3or the rotating shaft 6, causing the breakage or thermal deformation ofthe impeller 3 or the rotating shaft 6.

This problem can be avoided by designing and manufacturing appropriatelythe heat pipe. Namely, the heat pipe serves to withdraw the heatgenerated when the working liquid sealed in the container under apredetermined reduced pressure evaporates, i.e. by the latent heat ofevaporation. Accordingly, it can not be cooled to a lower temperaturethan the boiled point of the working liquid under a predeterminedreduced pressure. Accordingly, by adjusting the pressure of the workingliquid to be hermetically sealed so that the boiling point of theworking liquid is higher than the dew-point, it is possible to preventthe dew condensation in the vicinity of the heat receiving portion 28.

In this embodiment, the non-magnetic partition wall 11 is disposed in aclearance between the fan shaft side magnetic coupling 9 and the motorshaft side magnetic coupling 10; the space surrounding the rotatingshaft 6 is hermetically sealed from the outer field by means of thenon-magnetic partition wall 11 and the casing 12, and an air coolingmeans is constituted by the heat receiving portion 28, the heattransporting portion 29 and the air cooling/radiating portion 30.

Namely, according to this embodiment, the hot combustible gas used in asolid oxide fuel cell can completely be sealed: It is possible to coolthe bearing and so on by air-cooling; operations can be conducted withonly the power source provided by the fuel cell system itself and it isunnecessary to provide a cooling water pump or a cooling means forcooling water. Thus, it is possible to obtain a hot-gas blowing fansatisfying the conditions in the application to the solid oxide fuelcell.

In the present invention, the rotating shaft and the bearing for thehot-gas blowing fan can preferably be cooled with the air-cooling meanscomprising the heat receiving portion 28, the heat transporting portion29 and the air-cooling/radiating portion 30. The air-cooling means isalso applicable to the cooling portion 5 of the hot-gas blowing fanshown in FIG. 1, and the water cooling means comprising thewater-cooling jacket can be substituted with the air cooling means.

FIG. 6 is a plane view showing a fifth embodiment of the presentinvention wherein a scroll 1, an evaporative portion 33, a heattransporting pipe 34, a bearing 7, a shaft sealing device 27, a heatinsulating layer 16, an air cooling/radiating portion 30 disposed abovethe evaporative portion 33 and fins 32 are shown in cross section. FIG.7 is a diagram viewed from an arrow mark Q in FIG. 6, in which thescroll 1, the evaporative portion 33, the bearing 7, the shaft sealingdevice 27, the heat insulating layer 16, a casing 12 and enclosed waterwere shown in cross section. Reference numeral 34 designates the heattransporting pipe and numeral 31 designates a cooling fan. FIG. 8 is across-sectional view taken along X-X in FIG. 7.

A space surrounded by double-cylinders is provided inside theevaporative portion 33. The heat transporting pipe 34 is a hollow pipe.The end of the pipe at the side of the air cooling/radiating portion 30is hermetically sealed and the end thereof at the side of theevaporative portion 33 is opened to communicate with the space formedinside the evaporative portion 33. The joining portion of the heattransporting pipe 34 to the evaporative portion 33 is hermeticallysealed. Namely, the space inside the evaporative portion 33 and theinside of the heat transporting pipe 34 form a unified space. In theunified space, water 35 is contained under a predetermined reducedpressure to an extent that the entirety of the inner cylindrical portionof the double cylinders is under the water whereby a so-calledtwo-phase-fluid flowing thermo-siphon heat pipe without a wick isformed.

When the evaporative portion 33 receives a heat flux from the hot gas toshow temperature rise, the water 35 under a reduced pressure evaporatesat, for example, 50° C. The latent heat of evaporating water generatedat this moment withdraws the heat flux received by the evaporativeportion 33. The produced water vapor rises in the unified space formedby the inner portion of the evaporative portion and the inner portion ofthe heat transporting pipe and reaches the air cooling/radiating portion30 to be cooled for condensation. The heat transported during thecondensation is transferred to the air cooling/radiating portion 30. Thewater cooled and condensed in the air cooling/radiating portion 30 isreturned to the evaporative portion 33 due to the gravity. The functionand structure of the air cooling/radiating portion 30 are the same asthose of the fourth embodiment.

In the evaporative portion 33, the inner cylinder portion of the doublecylinders constitutes a housing for holding the bearing 7 and the shaftsealing device 27. Since the inner cylinder portion is immersed in thewater enclosed in the evaporative portion 33, the temperature of thisportion can be kept substantially uniform whereby there is no risk ofgenerating a thermal strain and therefore, normal rotation and normalshaft sealing function can be assured.

In the fourth embodiment, the heat transporting portion 29 comprisingheat pipes and the heat receiving portion 28 are not formed in onepiece, and therefore, a heat resistance exists between the heatreceiving portion 28 and the heat transporting portion 29. On the otherhand, the fifth embodiment has the thermo-siphon heat pipes formed byunifying the evaporative portion 33 and the heat transporting pipe 34whereby there is no heat resistance between them. Accordingly, thetemperature of the evaporative portion is lower than the temperature ofthe heat receiving portion of the fourth embodiment.

The temperature of the evaporative portion of the fifth embodiment wasmeasured under the same condition as the fourth embodiment. As a result,the average temperature at the evaporative portion of the fifthembodiment was 75° C. whereas the average temperature at the heatreceiving portion of the fourth embodiment was 80° C.

FIG. 9 is a cross-sectional view taken along a side plane of a sixthembodiment of the present invention wherein reference numeral 1designates a scroll, 2 an inlet port of scroll, 36 a cover, 37 anapertured portion and 38 a supporter for supporting the cover,respectively.

When the hot-gas blowing fan is used for a solid oxide fuel cell, it isnecessary to satisfy specifications such as air volume, air pressure andso on by driving a small-sized impeller at a high speed rather thandriving a large-sized impeller at a low speed from restrictions withrespect to cost and installation space. However, if a foreign matterhits the impeller rotated at a high speed, there sometimes causes thebreakage or deformation of the impeller.

Accordingly, a dust collector for preventing a foreign matter having asize to cause breakage or deformation of the impeller from suckingthrough the inlet port 2 of the scroll, is required.

With respect to the relation between the impeller 3 driven at a highspeed and a danger of the breakage or deformation thereof at the time ofcollision of a foreign matter, which depends on sizes, the relation canbe obtained by experiments seeking the relation between acircumferential velocity of the outer diameter of the impeller, i.e.,the maximum collision speed and a particle size of the foreign matter.

When the allowable particle size of a foreign matter with respect to themaximum revolution speed of a usable fan is obtained throughexperiments, the terminal sedimentation speed of a foreign matter havingan allowable particle diameter can be obtained by calculation.

When the hot-gas blowing fan is set on the ceiling of a furnace in avertically downward direction, the dimension of an inner diameter of theinlet port 2 of the scroll is determined so that the flowing speed of ahot gas passing through the inlet port is smaller than the terminalsedimentation speed. Then, there is little possibility of sucking aforeign matter which may cause the breakage or deformation of theimpeller 3.

On the other hand, when the hot-gas blowing fan is set on the bottom ofthe furnace in a vertically upward direction or is set on a side wall ofthe furnace in a horizontal direction, it is necessary to determine sothat the flowing speed of the hot gas passing through the inlet port issmaller than the terminal sedimentation speed, and at the same time,care should be taken about the falling of a foreign matter to theimpeller 3.

FIG. 9 shows a case that the hot-gas blowing fan is set on the bottom ofthe furnace in a vertically upward direction. A hot gas is sucked fromthe inlet port 2 of scroll after passing through the apertured portion37. The flowing speed Vs of the hot gas passing through the aperturedportion 37 is determined depending on the capacity of sucking air of thefan and the surface area of the apertured portion.

When a foreign matter having the allowable particle diameter passesclosely near the outer periphery of the cover 36 from an upper portionat the terminal sedimentation speed Ws, the distance L forcing it towardthe apertured portion by the flowing speed Vs of the hot gas to theapertured portion during a time passing through the apertured portion 37having a height H is expressed by the following formula:L=H×Vs/WsSince the dimension D of the outer diameter of the cover 36 is increasedso as to satisfy the following formula with respect to the dimension d1of the inlet port 2 of the scroll, a foreign matter having a largerparticle diameter than the allowable particle diameter is not sucked.Further, a foreign matter falling directly above the inlet port 2 of thescroll does not invade into the inlet port 2:(D−d1)/2>L

As described above, by setting a very simple inertia dust collectorcomprising the cover 36 and the supporter 38 for supporting the cover 36at the inlet port 2 of the scroll, it is possible to prevent thebreakage or deformation of the impeller caused by the sucking orinvasion of a foreign matter.

In this embodiment, the peripheral speed of the outer diameter of theimpeller is 205 m/sec and the weight of a foreign matter which may causethe breakage of the impeller made of silicon carbide is 0.001 gaccording to experiments. Since the foreign matter assumed in thisembodiment is a castable refractory having a specific gravity of 2.3g/cm³, the allowable particle diameter is calculated to obtain 1 mm.

The formula to calculate the terminal sedimentation speed Ws isexpressed by the following formula (refer to formula (11·4) and formula(11·7), P. 170 “Hydraulic Losses in Pipes and Ducts” published by JapanSociety of Mechanical Engineers, 1979):Ws={4×{(ρs/ρa)−1}×g×ds/3/Cd}^0.5Cd=11/Re^0.5where ρs represents the density of a foreign matter, ρa represents thedensity of a hot gas, ds represents an allowable particle diameter andRe represents Reynolds number. By substituting numerical values into theabove-mentioned formulas, the terminal sedimentation speed Ws=8.1 m/secwas obtained. In this embodiment, the volume of sucked air was 15m³/min, the dimension d1 of the inlet port 2 of the scroll was 0.2 m andthe height H of the apertured portion 37 was 0.1 m.

Based on the values of d1 and H, the flowing speed of the hot gas iscalculated so that Vs=4 m/sec, and the value of L is calculated to be0.05 m. Accordingly, the dimension D of the outer diameter of the cover36 was determined to be D=0.35 m because a dimension of outer diameterof at least 0.3 m was needed.

When the hot-gas blowing fan is applied to a solid oxide fuel cell, andif an abnormal process control takes place, local combustion of the hotcombustible gas may occur in the process. In such a case, flames of thelocal combustion contact directly the impeller, or the impeller suffersluminous flame radiation from the flames to be overheated, whereby anexcessively large thermal stress creates in the impeller and thebreakage or deformation of it may be caused.

The provision of the cover 36 at the inlet port 2 of the scroll preventsflames from extending to the impeller or the overheating due to theluminous flame radiation even in such case. The cover 36 used preferablyis not only of a plate structure but also of a grid structure made ofpipes or a heat-resistant metallic wire mesh, having a large heatcapacity.

When the cover 36 is used to reduce the production of a thermal stress,the hot-gas blowing fan can be set in a vertically downward direction ora horizontal direction, both cases being effective.

FIG. 10 is a cross-sectional view taken along a side plane of a seventhembodiment of the present invention wherein reference numeral 1designates a scroll and numeral 2 designates an inlet port of thescroll.

FIG. 10 shows a case that the hot-gas blowing fan is set on a side wallof a furnace to be extended horizontally in the furnace. When thedimension d2 of the inner diameter of the inlet port 2 of the scroll isdetermined so that the flowing speed Vc of a hot gas passing through theinlet port 2 of the scroll is smaller than the allowable terminalsedimentation speed Ws and the relation of the dimension K as thedifference between the length of the upper side and the length of thelower side of the inlet port 2 of the scroll is given by the followingformula, there is little possibility that a foreign matter having alarger particle diameter than the allowable particle diameter is suckedinto the inlet port 2 of the scroll:K>d2×Vc/Ws

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it is possibleto obtain a simple, completely gas-tight sealing means without using theutility other than the power source and a cooling means using coolingair. When the hot-gas blowing fan of the present invention is used for asolid oxide fuel cell, it is possible to obtain operations of highstability and high efficiency for a long term. Further, the applicationof the hot-gas blowing fan to various kinds of furnace for heating orfiring for industrial use can be accelerated, and it contributes toimprovement of thermal efficiency and quality.

1. A hot-gas blowing fan, comprising: a heat resisting impeller cantilevered by a rotating shaft; a bearing attached to the rotating shaft; a heat insulating layer disposed between the impeller and the bearing, the heat insulating layer including a first radial face that faces the impeller and an inner circumferential face that faces the rotating shaft; a cooling portion disposed between the heat insulating layer and the bearing, and the cooling portion includes a cooling fluid to remove heat from the bearing and the rotating shaft without contacting the bearing or the rotating shaft; a first magnetic coupling disposed on a shaft end of the rotating shaft at a side opposite to the impeller; a second magnetic coupling configured to be mated with the first magnetic coupling and disposed on a shaft end of a driving shaft of a motor; a non-magnetic partition wall disposed between the first magnetic coupling and the second magnetic coupling; and a collar positioned between the first radial face of the heat insulating layer and the impeller and positioned between the inner circumferential face of the heat insulating layer and the rotating shaft, wherein the collar comprises a different material than the heat insulating layer such that the collar prevents the heat insulating layer from contaminating a process gas flowing inside the hot-gas blowing fan, wherein a space surrounding the rotating shaft is hermetically sealed from an exterior of the hot-gas blowing fan by the non-magnetic partition wall and a casing.
 2. The hot-gas blowing fan according to claim 1, wherein the hermetically sealed space is filled with an inert gas.
 3. A hot-gas blowing fan, comprising: a heat resisting impeller cantilevered by a rotating shaft; a bearing attached to the rotating shaft; a heat insulating layer disposed between the impeller and the bearing, the heat insulating layer including a first radial face that faces the impeller and an inner circumferential face that faces the rotating shaft; a heat receiving portion disposed between the heat insulating layer and the bearing, and the heat receiving portion includes a cooling fluid to remove heat from the bearing and the rotating shaft without contacting the bearing or the rotating shaft; an air cooling/radiating portion provided at an outer side of a casing; a heat transporting portion connecting the heat receiving portion to the air cooling/radiating portion, wherein the heat transporting portion is a heat pipe; and a collar positioned between the first radial face of the heat insulating layer and the impeller and positioned between the inner circumferential face of the heat insulating layer and the rotating shaft, wherein the collar comprises a different material than the heat insulating layer such that the collar prevents the heat insulating layer from contaminating a process gas flowing inside the hot-gas blowing fan.
 4. The hot-gas blowing fan according to claim 3, wherein the heat receiving portion and the heat transporting portion are unified to form a thermo-siphon heat pipe.
 5. The hot-gas blowing fan according to claim 1, wherein the cooling portion includes a heat receiving portion disposed between the heat insulating layer and the bearing, and the heat receiving portion is connected to an air cooling/radiating portion provided at an outer side of the casing via a heat transporting portion.
 6. The hot-gas blowing fan according to any one of claims 1 to 5, further comprising: an inertia dust collector provided at an inlet port of a scroll.
 7. The hot-gas blowing fan according to claim 1, wherein the hot-gas blowing fan is configured to be attached to a solid oxide fuel cell.
 8. The hot-gas blowing fan according to claim 3, wherein the hot-gas blowing fan is configured to be attached to a solid oxide fuel cell.
 9. The hot-gas blowing fan according to claim 1, further comprising: a heat insulating spacer disposed between the collar and the cooling portion to block heat transfer between the collar and the cooling portion.
 10. The hot-gas blowing fan according to claim 3, further comprising: a heat insulating spacer disposed between the collar and the heat receiving portion to block heat transfer between the collar and the heat receiving portion.
 11. The hot-gas blowing fan according to claim 1, wherein a temperature of the cooling fluid is higher than a temperature of a dew-point of the process gas blown by the hot-gas blowing fan.
 12. The hot-gas blowing fan according to claim 3, wherein a pressure in the heat receiving portion is adjusted so that a boiling point of the cooling fluid is higher than a dew-point of the process gas blown by the hot-gas blowing fan.
 13. The hot-gas blowing fan according to claim 1, wherein the heat insulating layer is comprised of a ceramic fiber and the collar is comprised of stainless steel, heat-resistant cast steel, or ceramic.
 14. The hot-gas blowing fan according to claim 3, wherein the heat insulating layer is comprised of a ceramic fiber and the collar is comprised of stainless steel, heat-resistant cast steel, or ceramic. 